Re: PING^1 [PATCH v3] sched: Change no_real_insns_p to no_real_nondebug_insns_p [PR108273]

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Nov 10, 2023 at 12:25 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
>
> On Thu, 9 Nov 2023, Jeff Law wrote:
>
> > > Yeah, I noticed that the scheduler takes care of DEBUG_INSNs as normal
> > > operations.  When I started to work on this issue, initially I wanted to try
> > > something similar to your idea #2, but when checking the APIs, I realized
> > > why not just skip the basic block with NOTEs and LABELs, DEBUG_INSNs as
> > > well.  IMHO there is no value to try to schedule this kind of BB (to be
> > > scheduled range), skipping it can save some resource allocation (like block
> > > dependencies) and make it more efficient (not enter function schedule_block
> > > etc.), from this perspective it seems an enhancement.  Does it sound
> > > reasonable to you?
> > It sounds reasonable, but only if doing so doesn't add significant
> > implementation complexity.  ie, the gains from doing less work here are likely
> > to be very marginal, so I'm more interested in clean, easy to maintain code.
>
> I'm afraid ignoring debug-only BBs goes contrary to overall var-tracking design:
> DEBUG_INSNs participate in dependency graph so that schedulers can remove or
> mutate them as needed when moving real insns across them.

Note that debug-only BBs do not exist - the BB would be there even without debug
insns!  So instead you have to handle BBs with just debug insns the same you
handle a completely empty BB.

> Cc'ing Alexandre Oliva who can correct me on that if necessary.
>
> Alexander